mp - CHEM 267 Week 1 Melting Points(revised 7/10 For...

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CHEM 267. Week 1. Melting Points . (revised 7/10). For background information on determining MPs, do the assigned reading. You will use a Mel-Temp device. It is not necessary to read about the other MP devices. View the MP movie on the course website. The purpose of the Melting Point experiment is to learn to determine melting points (MPs) accurately. This is an important technique that will be used in many of the experiments in the Organic Lab. Always record a MP range - the temperature at which the first drop of liquid appears, to the temperature at which all sample has melted. Note that upon heating, crystals may expand or contract, resulting in movement of the crystals. This should not be mistaken for the beginning of the MP range. Wait for the first tiny drop of liquid to appear on the crystals. A wide MP range indicates that the sample is impure. A MP determination provides two important pieces of information: a physical constant, which can help to identify a compound, and a measure of the purity of a compound. Note too that an impure sample melts at a temperature lower than that of the pure compound. An impure sample therefore melts over a wide range and at a temperature lower than that of the pure material . For your purposes, a compound with a MP range of 2° C or less will be considered to be sufficiently pure. Apparatus : The height of sample in the capillary tube should be about 2-3 mm (the thickness of two 25 cent coins is about 3 mm). Three capillaries can be heated at the same time, although when learning to determine MPs it is advisable to do one at a time. Heating is accomplished by adjusting the voltage control - note that the settings are not temperature settings. They are given either in volts or in units of 0 to 10, where 0 means zero voltage and 10 means full voltage.
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